1. Field of the Invention
The present invention relates generally to an alignment fixture for an optical instrument such as an optical correlator, providing for the precise adjustment of the alignment of an element of the optical instrument at least along two transverse x and y axes, and also rotationally .theta. in roll about a z axis perpendicular to the x and y axes. Moreover, the alignment fixture can also provide for additional alignment adjustments, such as angular adjustments about the x and y axes, and possibly also a translational adjustment along the z axis. More particularly, the subject invention pertains to an alignment fixture as described providing for the precise adjustment and alignment of an element, such as a matched filter or multiple matched filter, in an optical correlator employing such matched filters as its optical memory, or of a multiple holographic Fourier transform lens therein.
The present invention can be particularly used with an Alignment System For An Optical Matched Filter Correlator as disclosed and claimed in U.S. patent application Ser. No. (216399), filed July 7, 1988.
2. Discussion of the Prior Art
A matched filter optical correlation system is disclosed in U.S. patent application Ser. No. 814,209, filed Dec. 27, 1985 now abandon, relative to which the alignment fixture of the present invention was designed and developed. The optical correlation system disclosed therein optically compares an input image with optical information stored in multiple matched filters to provide identification, position, and aspect information about the input image. In one disclosed embodiment, the input image is directed onto a spatial light modulator to spatially modulate a coherent beam of radiation. The spatially modulated radiation beam is directed onto a multiple holographic lens which performs a multiple number of Fourier transformations thereon to obtain an array of a multiple set of Fourier transforms of the spatially modulated radiation beam. A corresponding array of matched filters has the array of Fourier transforms incident thereon, with each matched filter comprising a Fourier transform hologram of a scale or an aspect view of an object of interest. Each matched filter passes an optical correlation signal in dependence upon the degree of correlation of the Fourier transform of the spatially modulated radiation beam with the Fourier transform hologram recorded thereon. An inverse Fourier transform lens receives the optical correlation outputs of the array of matched filters, and performs an inverse Fourier transformation on the optical correlation outputs. A detector detects the inverse Fourier transform of the optical correlation outputs, and produces a detector output signal representative thereof, which is generally maximized as alignments are adjusted in x, y and .theta. (rotationally in roll).
One problem with this type of optical correlator is that of obtaining a proper and precise alignment (x, y and .theta. rotational) of each individual matched filter with the particular Fourier transform incident thereon. A typical matched filter optical correlator as described hereinabove is normally initially set or adjusted such that, with respect to the matched filter therein, the axial distance along the z axis (optical axis), the .gamma. (pitch) adjustment, and the .beta. (yaw) adjustment are properly set, and these adjustments generally remain properly set and aligned in particular embodiments of the optical correlator. Accordingly, the initial adjustments of the matched filter with respect to z, .gamma. and .beta. are normally properly retained by the optical correlator (if the matched filter holder is designed initially with this requirement), and after the initial alignment adjustments, do not require re-adjustment each time a new matched filter is placed therein. However, when a new matched filter is placed in a typical optical correlator, precise adjustments and alignments are normally required along the x axis, the y axis, and the .theta. (roll) axis.